This invention relates to an apparatus which controls the rate of fluid flow through a closed or partially closed hydraulic system. In particular, this invention concerns an apparatus which controls the rate of fluid flow at a surgical site, thus preventing the occurrence of a fluid surge, the sudden increase of vacuum within a surgical cavity and the collapse thereof.
The delicate structures within the surgical cavity, such as an iris, cornea or lens capsule which surround the human lens in the case of the eye, or the walls of the human gallbladder or ureter in cases of stone removal, or the walls of the human arteries in cases of removal of arterial plaque, or the lining of joints in cases of tissue removal therefrom, can experience severe damage from such a collapse.
This invention relates particularly to the field of eye surgery in which material such as a cataract is removed from the eye, and other types of surgery involving the removal of material from within a surgical cavity by the use of fluid flow and aspiration methods. Devices for this purpose exist in the field of eye surgery, as well as surgery involving stone removal from the gallbladder, kidneys, or ureters. Such methods have also been utilized to remove obstructions from arteries.
Ultrasonic or laser and/or mechanical cutting are employed to reduce the unwanted material to a size which may flow uninhibited through the aspiration conduit. However, such material may not always be invariably reduced to an appropriate size, thus resulting in an obstruction in the aspiration conduit.
A fluid surge at the surgical cavity generally occurs pursuant to two events. One such event is when an obstruction, as aforementioned above, is released. The other such event is when trapped air creates uncontrolled aspiration forces within the aspiration conduit.
The sudden release of an obstruction, which may occur at any location in the pre-pump aspiration conduit, results in the occurrence of a fluid surge. As the obstruction impedes fluid flow within the aspiration conduit, the pump employed by the system continues to operate, thereby increasing the vacuum in the pre-pump conduit. Upon release of the obstruction, a fluid surge develops and travels from the surgical cavity into the aspiration conduit. The fluid surge is caused by the aforementioned decrease in vacuum and a rebound of the aspiration conduit which had partially collapsed in response to the vacuum within it.
Other reasons for the occurrence of the fluid surge include the expansion and contraction of air which may at times gain access to the aspiration conduit. A fluid surge may be caused by the sudden contraction of air within the aspiration conduit upon release of an obstruction, when such air had previously expanded during obstruction of the aspiration conduit.
Generally, fluid aspiration devices require the use of a flexible conduit as well as containers to collect the aspirated fluid and/or material. Such devices may also employ mechanisms whereby the flexible conduit may be vented to the atmosphere in order to release accumulated vacuum within the tubing.
The elasticity of the aspiration conduit as well as the air spaces within the container used for collection and/or air introduced into the system during operation may act to create forces which may collapse or expand the conduit and thereby create undesirable, uncontrolled aspiration forces within the system. This can result in periods of undesirable and dangerously increased flow through the aspiration system, with subsequent loss of pressure within the surgical cavity being treated and the collapse thereof.
Various prior art devices have been disclosed for controlling fluid flow and the direction thereof during the removal of material from within the surgical cavity. However, devices employing the automated reversal of a pump, in combination with a pressure transducer and logic system, have not been disclosed.
Mechanisms currently in existence to prevent a fluid surge include intermittent venting of fluid into the aspiration conduit from another source. Such systems require a second source of fluid and shunting valves which may be costly to manufacture and/or more prone to failure than the aspiration system described herein. The apparatus disclosed in this specification is safer, less costly to manufacture, and more efficient than the other fluid control system.
U.S. Pat. No. 4,705,500 to Reimels discloses an aspiration-irrigation system, utilizing a peristaltic pump and a foot operable control unit which controls the speed and rotational direction of the pump. The control unit essentially consists of a foot pedal and a control box.
The rotational direction of the pump is a function of the depression of the pedal. Rotation of the pump counter-clockwise creates a negative pressure within the aspiration. port, causing aspiration of fluid/tissue particles, while rotation of the pump clockwise creates a positive pressure for ejection of blockage particles.
Although Reimels recites a pump which reverses rotation, it does not disclose or suggest a pressure transducer or a logic system, which senses pressure changes and transmits such information to the pump, which may then automatically reverse its rotation as described in this application. Rather, the operator must manually reverse the rotation of the pump by varying the amount of pressure on the pedal.
U.S. Pat. No. 4,832,685 to Haines discloses an irrigation-aspiration apparatus consisting of an aspiration conduit, a peristaltic pump, and a pressure transducer connected to the aspiration conduit. The pressure transducer generates an electrical signal proportional to the vacuum in the aspiration conduit.
An obstruction in the aspiration is indicated by the vacuum exceeding a pre-set level, whereby the pressure transducer shuts off the pump. The obstruction is ejected from the aspiration conduit by equalizing the pressures in an irrigation conduit and the aspiration conduit, which is accomplished by filing the conduit system with liquid. As soon as the pressure is equalized, the pressure transducer detects the lower level of suction and restarts the pump.
Although Haines recites a peristaltic pump and a pressure transducer, it does not disclose or suggest that the pump reverses rotation upon the vacuum exceeding a predetermined value.
U.S. Pat. No. 4,180,074 to Murry discloses an irrigation-aspiration device comprised of an aspiration tube, a peristaltic pump, a pressure transducer, and a diaphragm. Although Murry recites a peristaltic pump and a pressure transducer, it does not disclose reversal of the peristaltic pump when a blockage of the aspiration tube occurs.
Additionally, U.S. Pat. No. 4,493,698 to Wang discloses a method for controlling the vacuum level in a debris receptacle and aspiration conduit during surgery. Such method primarily consists of an aspiration conduit, a peristaltic pump, a pressure transducer, potentiometers, and a controller.
The system's vacuum is pre-set by the potentiometer, which sends signals of the desired vacuum level to the controller. The controller receives the signal of the actual vacuum in the aspiration conduit from the pressure transducer and adjusts the opening of valves in order to maintain the desired pressure in the aspiration conduit.
Like the aforementioned patens of Murry and Haines, Wang does not disclose or suggest the reversing of the pump'rotation when an occlusion occurs.
U.S. Pat. No. 4,798,580 to DeMeo discloses an irrigation and aspiration system. However, it does not disclose a pressure transducer nor the reversal of the pump when an occlusion in the aspiration conduit occurs.